Pen type drug delivery devices have application where regular injection by persons without formal medical training occurs. This may be increasingly common among patients having diabetes where self-treatment enables such patients to conduct effective management of their disease. In practice, such a drug delivery device allows a user to individually select and dispense a number of user variable doses of a medicament.
There are basically two types of drug delivery devices: resettable devices (i.e., reusable) and non-resettable (i.e., disposable). For example, disposable pen delivery devices are supplied as self-contained devices. Such self-contained devices do not have removable pre-filled cartridges. Rather, the pre-filled cartridges may not be removed and replaced from these devices without destroying the device itself. Consequently, such disposable devices need not have a resettable dose setting mechanism.
A further differentiation of drug delivery device types refers to the drive mechanism: There are devices which are manually driven, e.g. by a user applying a force to an injection button, devices which are driven by a spring or the like and devices which combine these two concepts, i.e. spring assisted devices which still require a user to exert an injection force. The spring-type devices involve springs which are preloaded and springs which are loaded by the user during dose selecting. Some stored-energy devices use a combination of spring preload and additional energy provided by the user, for example during dose setting.
These types of pen delivery devices (so named because they often resemble an enlarged fountain pen) generally comprise three primary elements: a body cartridge section that includes a cartridge often contained within a housing or holder; a needle assembly connected to one end of the cartridge section; and a dosing section connected to the other end of the cartridge section. A cartridge (often referred to as an ampoule) typically includes a reservoir that is filled with a medication (e.g., insulin), a movable rubber type bung or stopper located at one end of the cartridge reservoir, and a top having a pierceable rubber seal located at the other, often necked-down, end. A crimped annular metal band is typically used to hold the rubber seal in place. While the cartridge housing may be typically made of plastic, cartridge reservoirs have historically been made of glass.
The needle assembly is typically a replaceable double-ended needle assembly. Before an injection, a replaceable double-ended needle assembly is attached to one end of the cartridge assembly, a dose is set, and then the set dose is administered. Such removable needle assemblies may be threaded onto, or pushed (i.e., snapped) onto the pierceable seal end of the cartridge assembly.
The dosing section or dose setting mechanism is typically the portion of the pen device that is used to set (select) a dose. During an injection, a spindle or piston rod contained within the dose setting mechanism presses against the bung or stopper of the cartridge. This force causes the medication contained within the cartridge to be injected through an attached needle assembly. After an injection, as generally recommended by most drug delivery device and/or needle assembly manufacturers and suppliers, the needle assembly is removed and discarded.
Typically, an injection device comprises a lead screw or piston rod, which is driven by a drive member during dose dispensing to act on a cartridge bung. If the lead screw rotates during dose dispensing, friction occurs with respect to the (rotationally static) cartridge bung. A bearing may be provided to minimize friction.
In a very simple form, a drug delivery device comprises a housing defining a longitudinal axis and having a tubular portion with an inner thread, a piston rod having a threaded portion with a distal end, and a bearing disc having a distal face and a proximal face. For example, the piston rod may be used for selecting and dispensing a number of user variable doses of a medicament from a reservoir in the housing or a cartridge.
WO 2010/139641 A1 discloses a spindle and bearing combination for use in a more complex drug delivery device comprising a rotatable spindle having a distal end and a disk-shaped bearing attached to the distal end of the spindle through a first connection comprising a web that fixedly attaches the bearing to the spindle to prevent independent movement of the bearing relative to the spindle. This first connection is replaced by a second connection which is created when the web is severed and the web is disconnected from the bearing.
Further, WO 2009/132781 A1 discloses a dosing mechanism which includes a piston rod of generally circular cross-section. A pressure foot is located at the distal end of the piston rod. The pressure foot is made of two separate parts which are snapped together around a distal end portion of the piston rod. The pressure foot is disposed to abut the proximal face of a piston.
Assembly of known drug delivery devices with a threaded housing part and a threaded piston rod typically requires relative rotation of the housing part and the piston rod. A rotational assembly movement is more complicated than a mere axial movement. Further, attachment of the pressure foot or bearing disc includes in some cases complex steps.